The present invention relates to a hybrid oven for cooking by hot air impingement and microwave cooking and a non-hybrid oven for cooking by hot air impingement, and more particularly to such an oven which is capable of rapidly cooking food products.
The "fast food" industry operates under the premise that, due to the anticipated sales volume during peak hours, food can be prepared before an order is placed therefor. As a result, the food is usually delivered to the customer within 30 seconds of the order because the food was already prepared, typically within the last five minutes so that its quality is not degraded. However, this results in substantial inventory loss if customer traffic is less than anticipated, as well as substantial delays if customer traffic is more than anticipated, especially during off-peak hours.
A similar problem exists within food service venues other than typical "fast food" restaurants. For example, prepared food sold in grocery stores and convenience stores is typically prepared several hours before the food is purchased by the consumer. Not only does this result in substantial inventory loss if traffic is less than expected, but the food itself is often of lower quality than what might be available from a restaurant because it has been prepared well in advance of sale to the consumer and held in anticipation of sale. This reduced quality, as well as the perception of reduced quality in the minds of consumers, results in lower sales than would occur if the food quality was in line with what is cooked and immediately (or almost immediately) sold at restaurants.
Attempts to deliver "cooked to order" food of high quality within an acceptable time frame have not been entirely successful. Indeed, it is precisely this shortcoming which has prevented the creation of acceptable hot food vending machines (similar in size and concept to the well known soft-drink vending machines) which could turn out national fast food chain quality food from a fully automated machine.
A satisfactory quick-cooking oven must be able to heat or cook--from frozen, refrigerated or ambient temperature states--food products, whether they are already prepared (e.g., frozen fried chicken nuggets), partially prepared (e.g., frozen "par-baked" pizza) or raw (e.g., biscuits, fish), with the process generally being completed within times that the fast food customer has become accustomed to waiting (generally less than 30-50 seconds for most food products). It will be readily appreciated that an oven which can complete the process in 30 seconds can enable food to be sold at twice the rate during peak hours than a machine which requires a minute, whether the oven is disposed in a fast food restaurant, in a ancillary food service location such as in a convenience store, or as part of an automatic vending machine. Additionally, there is a threshold to the amount of time most consumers will wait for a food product to be delivered. Although there may be some debate as to what that threshold time limit is, it is clear that far fewer customers will knowingly wait for 90 seconds for delivery of their food than will wait for 30 seconds. This marginal customer group will also result in additional sales.
It will be appreciated that a quick-cooking oven is also desirable for many food items because various characteristics which change during the cooking process (such as texture, flavor, odor and appearance) may be affected in different ways during the cooking process--by which is meant, faster cooking times may in certain instances provide a higher overall quality food product than slow cooking times.
Conventional microwave ovens can deliver large amounts of heat over short periods of time, but result in a "synthetic" product, without browning or crisping. While this may be acceptable for some products, such as popcorn, it is generally unacceptable for a wide variety of food products such as pizzas, fried chicken, toast, etc. Conventional air impingement ovens can rapidly cook food products by forcing heated air onto the food surface at high velocities, thus "driving" the heat into the food product. However, attempts to reduce cook times in conventional air impingement ovens are limited in their effectiveness by the food product degradation which occurs as the temperature and velocity of the air striking the food product are increased.
One of the biggest challenges in rapid cooking is to deliver by hot air a consistent supply of energy to the food product, particularly as it relates to successive cooks of identical food products. This is a cooking quality issue. When large amounts of heat enter and leave a system quickly, there is almost always a "sine wave" effect. That would not necessarily be completely bad if the point on the sine curve at which food begins and ends each cook cycle was precisely repeatable. But an important goal is to have each cook be identical to the last one. Even if the same average number of calories is delivered during each cook cycle (e.g., by starting at a low temperature and finishing at a high temperature on one cook, and vice versa on the next cook), two different products may be produced. Accordingly, the heat delivered to the food product must be predictable along a relatively flat line.
Conventional hybrid ovens, which combine both hot air impingement and microwave cooking techniques, can heat and cook more rapidly than either cooking method individually. However, the known hybrid ovens are either much too slow (for example, requiring a lengthy period of as much as five minutes to cook a frozen pizza) or, if they have sufficient energy input (such as 220 volts) and/or are provided with a substantial warm-up time (frequently 15 seconds or so), they can cook the same food product in a faster but still unacceptably slow period (for example, 180 seconds). The 180 second ovens typically use as heating elements heating coils similar to a hair dryer, which take several seconds to reach peak temperatures and then only heat up the air as it passes over the heating coils. Thus such ovens require a substantial warm-up time to heat the coils to peak temperatures and then additional time to heat up the air already in the oven by passing it over the coils. (It should be kept in mind that the initial batch of hot air leaving the heating coils is rapidly cooled as it mixes with the cold food product and the air already present in the cooking chamber.) While a fast food restaurant will generally have sufficient energy to operate a powerful hybrid oven (such as 220 volts), other locations which might benefit from rapid cooking (such as a typical vending machine location) may have only a 110 volt power supply available to them and thus cannot utilize one of the hybrid ovens which requires a 220 volt power supply. Because heating coils and magnetron(s) which could operate simultaneously on a 110 volt power supply would be of substantially reduced capacity as compared to heating coils and magnetron(s) which each require an essentially dedicated 110 volt power supply to operate efficiently, a larger power supply (e.g., 220 volts) would be required to deliver similar cooking energy in the known hybrid ovens.
Non-hybrid hot air impingement ovens are typically not used in applications which require immediate cooking and delivery to the consumer, since the impinging hot air has only a limited ability to cook the food interior, especially where the product is of substantial dimensions. Even so, the non-hybrid hot air impingement oven of conventional design is subject to many of the same disadvantages as the hybrid oven, and in particular requires several minutes in order to cook the food by hot air impingement alone. These ovens, like the 180 second ovens, require a warm-up time of several seconds in order to reach peak temperatures in the heating coils, and then still more time in order to heat up the air already in the system by passing it over the heating coils.
Certain steps have been taken to reduce cook times in conventional microwave, air impingement and hybrid ovens. For example, microwave energy can be increased as a means of imparting more microwave energy to a food product over a given period of time, thus increasing the temperature of the food product more rapidly during that period of time. However, this increased heat transfer due to increased microwave energy also increases the product degradation that occurs when microwaves are used to heat food products. Air velocities and temperatures in conventional air impingement ovens can also be increased as a means of reducing cook times. In general, increasing the velocities of columnated jets of heated air, as well as increasing the temperature of the air, result in increased heat transfer. However, at some point the benefits of more rapid heat transfer into the good product are offset by a reduction in the quality of the food product. In fact, most conventional air impingement ovens require some type of movement of the food product relative to the columnated jets of heated air which impinge upon the food surface, at least in part for the purpose of minimizing the degradation of the food directly beneath the columnated jets. As a result of these and other limitations, the fastest microwave, air impingement and hybrid ovens of conventional design all have difficulty cooking food products at a quality level in line with fast food restaurants.
Conventional microwave ovens have the ability to deliver varying amounts of microwave energy to food products within their cavities, and for various cook times depending on operator input. This feature allows conventional microwave ovens to be used to heat a variety of food products, one after another, and to adjust the amount of microwave energy delivered to a particular type of food product based on operator input. Accordingly, the operator may press the "potato" button when heating a potato, and the "soup" button when heating soup, and expect different amounts of microwave energy to be delivered to the food products based on these different operator inputs. However, particular difficulty has been encountered in consistently heating food products of the same type, but varying sizes (such as 6 ounce versus 7 ounce potatoes), with microwave energy at a fixed setting. Conventional air impingement ovens have very little flexibility in both quantity and duration of heat transfer due to the fact that food typically travels through the cooking cavity on a support means (such as a conveyer) at a fixed rate. This not only makes it difficult to vary air velocity from one product to another, but also difficult to vary cook duration. Attempts to solve these problems by combining air impingement and microwaves in conventional non-conveyorized systems by varying air velocities and microwave energy under computer control, have not been entirely successful. Even the most advanced design of hybrid ovens of conventional design, with state of the art cooking controls, encounter particular difficulty in cooking a variety of products (such as chicken, pizza, egg rolls and french fried) one after the other, of the quality and at the speeds consumers demand and with any operational consistency.
Accordingly, it is an object of the present invention to provide a quick-cooking oven such as a hybrid oven generally capable of cooking most frozen foods of at least single entree portions within 30 to 80 seconds depending upon food product and volume.
It is another object to provide such a quick-cooking oven which is generally capable of cooking most refrigerated food products of at least single entree portions within 15 to 50 seconds, depending upon food product and volume.
Another object is to provide such an oven which in one embodiment utilizes both hot air impingement and microwave cooking.
It is also an object to provide such a quick-cooking oven which cooks food products which are generally at least of the quality of food served at fast food restaurants.
A further object is to provide such a quick-cooking oven which is generally capable of cooking a wide range of food products, one after another.
It is a further object of the present invention to provide in one embodiment a quick-cooking non-hybrid oven which cooks with hot air impingement only.
Another object is to provide such a quick-cooking non-hybrid oven which is generally capable of cooking most refrigerated food products of at least single entree portions within 20 to 60 seconds depending upon food product and volume.
It is also an object to provide such a quick-cooking non-hybrid oven which cooks food products which are generally of at least the quality of food served at fast food restaurants.
A further object is to provide such quick-cooking non-hybrid oven which is generally capable of cooking a wide range of good products, one after another.
Another object is to provide such an oven which cooks foods of the same type to a consistent quality throughout the day, regardless of the order in which various foods are cooked.
It is a further object to provide such an oven which is safe, simple and economical to manufacture, use and maintain.